1. Field of the Invention
The present invention relates to a gas transportation method for grain, and more particularly to a method for transporting grain with low hardness such as rice by means of gas.
2. Description of Related Art
Conventionally, in rice polishing factories and boiled rice factories, delivered unpolished rice is usually polished by a rice polishing machine to be half-polished rice, and the half-polished rice is processed to be polished rice with its rice bran removed. This polished rice is stored, blended with various kinds of polished rice and wrapped to be shipped, or is used immediately for boiled rice. In various transportation processes of transporting rice from an unpolished rice storage tank to the rice polishing machine, from the rice polishing machine to a rice bran removing machine, from the rice bran removing machine to a polished rice storage tank, from the polished rice storage tank to a blended rice accommodation tank, and so on, a number of transportation apparatus such as bucket conveyers, lifts, horizontal belt conveyers, and the like are usually used.
However, these transportation apparatus tend to become upsized as factories become large, which has resulted in difficulty in assembly, installation, and maintenance thereof. Furthermore, since rice bran remains in gap parts in these transportation apparatus, microbes such as mold may grow to gather insects and so on eating the mold. This has brought about a problem that values of rice and boiled rice as products may possibly be lost. Since the transportation apparatus need to be frequently disassembled for cleaning in order to eliminate the problem, a problem has been further caused that maintenance cost is increased.
To solve these problems, apparatus for pneumatically transporting rice through pipes are known as are disclosed in Japanese Patent Laid-open No. Hei 7-330151, Japanese Patent Laid-open No. Hei 2-56255, and Japanese Patent Laid-open No. Sho 52-20582. In these apparatus, grain such as rice is transported by air streams which are generated in pipes with the use of blowers and compressors. The use of such a pneumatic transportation method makes it possible to avoid the problem that the rice bran remains halfway in the pipes since the rice and the air are transported in the pipes which are shielded from the outside.
However, in the conventional pneumatic transportation method, problems have often occurred that transported rice is crushed or each grain of rice cracks to reduce the value of the rice as a product. Since consumers demand high quality, particularly for rice to be used for boiled rice, sufficient quality control is required. However, it has been very difficult to transport rice pneumatically without causing any crush or crack to the rice.
The present invention is made in view of the conventional problems as described above and it is an object of the present invention to provide a gas transportation method and apparatus which are capable of preventing transported grain such as rice from crushing or cracking.
Transportation methods by means of gas such as air are generally divided into a high-pressure transportation method in which the pressure of supplied air is set at a value equal to 200 kPa (kilopascal) or more and a low-pressure transportation method in which the pressure of the supplied air is suppressed at a low value. In the high-pressure transportation method, pressurizing air flows through transportation pipes at a high speed when transportation is finished so that substances moving though the pipes may possibly collide with inner wall surfaces of the pipes to be crushed. Hardness of grain such as rice is generally in a lower range of 11xe2x89xa6Hvxe2x89xa614 in terms of Vickers hardness Hv and since crush and crack of grain during transportation affect its quality, the low-pressure transportation method in which the pressure of the supplied air is suppressed at a low value is appropriate for pneumatic transportation of grain. However, when grain is transported through pneumatic transportation pipes in which transportation passages are long and curved, pressure loss is caused. Therefore, making allowance for this pressure loss, air pressure of a supplying source is generally set at approximately 50 kPa. Transportation of grain through the pipes under this pressure causes the possibility that the grain may be damaged, and therefore, a countermeasure for this problem is required.
Next, findings obtained by the inventors of the present invention are explained. As a result of various studies on correlation of a collision speed of polished rice with its crushing rate and cracking rate, the inventors of the present invention have found that a velocity V of transportation gas needs to be in a range from 10 m/s to 20 m/s. FIG. 1 is a graph showing correlation between a collision speed and rates of occurrence of crushed granules of polished rice and of occurrence of cracked plus crushed granules of polished rice. Here, the crushed granules of polished rice mean polished rice which is crushed to be broken into pieces and therefore, is difficult to be used as boiled rice and can be used only for materials for confectionary, rice crackers, or the like. The cracked granules mean polished rice which only has cracks therein and can be used as boiled rice. This experiment was conducted, using a device in which a blower 82 is disposed at one end of an acryl pipe 81 having length of 1000 mm and a stainless plate 83 is disposed vertically in a position 25 mm away from an exit at the other end of the acryl pipe 81, as shown in FIG. 2. Damage condition of polished rice 84 was examined after the polished rice 84 was put at an end part on a blower 82 side inside the acryl pipe 81 as shown in FIG. 2 and was pneumatically transported by the blower 82 to be collided with the stainless plate 83 at a collision angle of 90 degrees.
It is apparent from FIG. 1 that the occurrence rate of crushed granules or cracked and crushed granules of the polished rice suddenly increases when the collision speed exceeds 20 m/s. Therefore, the velocity V of the transportation air needs to be set at a value equal to 20 m/s or less. Meanwhile, in order to secure an amount of transported rice in pneumatic transportation, the velocity V of the transportation air needs to be set at a value equal to 10 m/s or more. Based on the above findings, it has been found that the velocity V of the transportation air needs to be set at a value in a range of 10 m/sxe2x89xa6Vxe2x89xa620 m/s.
The inventors of the present invention have also obtained correlation of a difference in temperature between polished rice and transportation air with damage to the polished rice under the condition that the velocity V of the transportation air is fixed (V=20 m/s), using the experiment device shown in FIG. 2. In this experiment, the polished rice 84 is put and kept unmoved in the air whose temperature is 20xc2x0 C. and whose humidity is 70%, and thereafter, the polished rice 84 whose temperature has reached 20xc2x0 C. is put at one end on the blower 82 side of the acryl pipe 81, while an air stream generated by the blower 82 is supplied with its temperature adjusted by a heater 85 to vary its difference in temperature from that of the polished rice 84. Similarly to the aforesaid experiment, the damage condition of the polished rice 84 was examined after the polished rice 84 was pneumatically transported by the blower 82 to be collided with the stainless plate 83 at the collision angle of 90 degrees.
The result of the experiment is shown in FIG. 3. In FIG. 3, the horizontal axis shows a difference in temperature (xc2x0C.) between the polished rice and the transportation air and the vertical axis shows an occurrence rate of crushed granules and an occurrence rate of cracked granules of the polished rice. The occurrence rate of crushed granules is shown by the solid line A and the occurrence rate of cracked granules is shown by the broken line B.
It is apparent from FIG. 3 that a crushing rate of the polished rice varies depending on the temperature difference between the polished rice and the transportation air. For example, the result of the experiment in FIG. 1 shows that the crushing rate of the polished rice is approximately 15% under the condition of the velocity of V=20 m/s, but the result of the experiment in FIG. 3 shows that the crushing rate of the polished rice increases to approximately 22% or more under the condition that the temperature difference between the polished rice and the transportation air is 20xc2x0 C. or more.
The inventors of the present invention have found from the experiment result shown in FIG. 3 that crushed granules do not occur when the temperature difference between the polished rice and the transportation air is 10xc2x0 C. or less. Therefore, when the polished rice is transported by transportation air flowing through transportation pipes which are connected with tanks for accommodating the polished rice therein, it is appropriate that the transportation air whose temperature difference from that of the polished rice flowing into the tanks or the polished rice flowing out of the tanks is 10xc2x0 C. or less is supplied into the transportation pipes to transport the polished rice. Basically, it is appropriate that the temperature of the transportation air is equal to the temperature of the polished rice, but it has been found that in an actual apparatus, the temperature difference of the transportation air from that of the polished rice may be within a range of xc2x115xc2x0 C., and more appropriately, within a range of xc2x110xc2x0 C.
The present invention, which is made based on these findings, is a transportation method for grain which is characterized in that it measures the temperature of transported grain and controls the temperature of transportation gas so that a difference between the measured temperature of the grain and the temperature of the transportation gas is adjusted to be in a predetermined range, when the grain is transported by means of gas flowing through a transportation pipe.
The difference between the measured temperature of the grain and the temperature of the transportation gas is appropriately within a range of xc2x115xc2x0 C. Furthermore, it is appropriate that the humidity of the transportation gas is controlled to be substantially equal to equilibrium humidity of the grain.
It is appropriate that the grain is rice.